AEROSPACE MEDICINE - SOME USEFUL TIPS

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Hi friends, As part of my three year training for my postgraduate degree in Internal and Emergency Medicine, I am currently posted in the Department of Aerospace Medicine for 1 month. It is much less hectic than Cardiology and Neurlogy postings, so I guess I will get more time to fool around with FS2002. :-hahI hope you will find this article useful. I have covered some commonly asked topics by my patients and of course my Professor during our Outpatient sittings.(1) Jet lag(2) Travelling with kids(3) Why your ears hurt(4) Gynaecological problems(5) Vaccination(6) Some miscellaneous topicsJET LAG.Jet lag is caused by traveling at great speeds over many time zones. This unbalances the "circadian rhythms," or biological lock, which is set by the pineal gland (a tiny organ in the brain). Eye cells send light and darkness messages to this gland, which releases melatonin (a sleep-inducing hormone) in response to darkness. Thus, abrupt changes in time zones can upset melatonin production, which ultimately unbalances the body's sleep-wake cycle. These biological functions, combined with travel-related physical and emotional stress, cause jet lag. Common symptoms of jet lag include headaches, irritability, upset stomach, sleeplessness, gastric discomfort, chills and inability to concentrate. Symptoms may be worse if you are traveling west to east (away from the sun), because light helps to preserve the body's equilibrium. Travel from east to west (to an earlier time zone) results in fewer jet lag symptoms, and traveling northward or southward does not affect the body's circadian rhythms at all. Experts say it takes one day for every time zone crossed to recover from jet lag symptoms. For example, if you cross six time zones, it will take six days to feel like your old self again. Although there are many methods for minimizing jet lag, it is impossible to eliminate it entirely. One suggested method of minimizing jet lag effects is to drink plenty of water before, during and after the flight. Some doctors recommend that you drink two eight-ounce glasses of water right before departure. Dehydration is highly possible during airplane travel, due to dry cabin air. It results in diminished blood flow to your muscles, reduced kidney functions and fatigue, all of which induce jet lag. You can prevent dehydration by drinking one liter of water for every six hours of flight in addition to beverages you drink with meals. Even if you may not be thirsty, it is important to drink water on a regular basis throughout the flight, because the body's thirst mechanism does not warn you early about dehydration. Researchers are now looking into "light therapy," which is a method of re-adjusting the body's inner clock by controlling exposure to natural and artificial full spectrum light. One step in this strategy is to expose yourself to daylight as soon as possible once you arrive at your destination. Researchers also advise that you turn on your overhead light during your flight when it is daylight at your destination and turn off your light, or wear an eyeshade, when it is night there. A second strategy is to try to reset the body's clock through the use of food. Many airlines have started serving their meals according to the destination's time zone. However, the "jet lag diet," another food strategy once thought to play an important role in minimizing the effects of jet lag, has been proven ineffective. Another recent research strategy suggests melatonin capsules as a possible method of combating jet lag fatigue. Melatonin is a hormone marketed as a dietary supplement to assist with sleep and jet lag. Melatonin is a naturally produced in the pineal gland. Concentrations in the blood vary throughout the day. Levels are higher during the hours of sleep and lower during the waking hours. The amount of ambient light seems to control this variation. Following a few simple "do's and don'ts" can help: Don't smoke, drink large amounts of alcohol, or take unnecessary medication while in flight. Do get a decent night's sleep before your flight. Do try to get some sleep during long flights. Do exercise while on board the plane by stretching, walking about the cabin, and doing fitness exercises in your chair (like squeezing a tennis ball for seven counts and then releasing)Much of the stiffness and the uncomfortable, dazed feeling following a flight is simply the result of sitting inactively for long periods of time. You may want to ask airline representatives if they can provide a brochure for in-flight exercises.Finally, limiting your activities the first day after your arrival will yield more hours of fun and productivity in the end.

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PART II - TRAVELLING WITH KIDS.Children under the age of 2 years travel free on most airlines, but this means that they may have to sit on your lap if the plane is full. When you make your reservations, try to avoid a full flight. If you can, schedule your flight to avoid the busiest times of day at airports (8 to 10 AM, 4 to 7 PM). If possible, reserve a bulkhead seat (just behind the bulkhead that separates coach and first class), since it has the most room. If you have to change planes, be sure to schedule enough time for the connection. Car rental agencies generally have infant seats available with their cars. You need, however, to reserve the satety seat when you reserve the car. It is also wise to call ahead to the local agency where you will pick up the car to confirm that the car seat is available. The flight attendants can warm food and bottles for you. Be sure to also bring small snacks your baby can nibble on and play with: Cheerios, bagels chips, etc. (ASSUMING HE/SHE IS OVER FOUR MONTHS BELOW WHICH IT IS COMPULSORY BREAST FEEDING ONLY!!)Check-in early so that you can get the baby settled before others board the plane. If you are traveling by yourself and won't be met at your destination, a portable stroller is a lifesaver. You can generally fold it up and take it on board with you.Diapering can be a hassle on the plane. Try to double-diaper or use ultra-absorbent diapers just before you board the plane. If you do change diapers on the plane, you can use an airsickness bag to dispose of them.For takeoff and landing, put the seat belt just around you and hold your baby on your lap or in a Snuggli (frontpack carrier). Don't place the seat belt around the baby. This, obviously, is for airplanes only, not for autos where the child must be placed in a proper car safety seat. Children over two will need to wear their own seatbelt on the airplane.In the older child prone to airsickness, it is usually okay to give Dramamine or an antihistamine one half hour before flying. If your child has a mild cold prior to flying you might consider giving some decongestant medicine beforehand. Younger infants could get an oral dose of Sudafed or similar product up to every 4 hours. Toddlers could get a dose of Children's Neo-Synephrine nasal spray up to every 6 hours. Older kids and teens can get a full adult dose (two sprays into each nostril) of Afrin (oxymetazolidine) adult-strength nasal decongestant spray up to every 12 hours.DO NOT TAKE ANY OF THESE WITHOUT CONSULTING YOUR PAEDIATRICIAN - THIS IS PURELY FOR YOUR INFORMATION.Airliner cabins maintain a constant atmospheric pressure above 8,000 feet altitude. Actually, there is no problem associated with taking off, climbing, flying as high as 45,000 feet, or descending to 8,000 feet. But, it's those last 8,000 feet to landing that creates problems for children's ears. Usually you can tell when your plane is passing below 8,000 feet because that is about the time when you'll see the stewardesses start to scurry around, making sure that everyone's seat belts are buckled, seatbacks are in their upright position, etc. That's your cue to start giving your child something liquid to drink. The swallowing will help to equalize the pressures in the ears while the plane is on final approach to landing. Older children above 8 years old can sometimes be taught to clear their ears on descent by having them close their mouths, pinch their nostrils, and swallow.Given all the equipment you have to carry when you travel with a baby, it is easiest to let other passengers deplane before you. Use this time to clean up your seat area before you leave. If worse comes to worst, and your child needs medical attention, there are usually many walk-in medical care centers near-by airports. Or, if you have relatives at your destination, they may be of help in selecting urgent medical care for your child

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PART III - WHY YOUR EARS HURTBarotitis media is the most common problem associated with aerospace travel. Barotitis media consists of a traumatic inflammation secondary to a pressure differential between the air in the tympanic cavity and mastoid air cells and that of the ambient air (cabin pressure). Patients may report ear popping during climbs, but severe ear blocks requiring corrective maneuvers usually are limited to descent or increasing cabin pressurization. Physiologically, the eustachian tube must ventilate the middle ear and equalize pressure. The anterior two thirds of this organ is membranocartilaginous and typically rests in the closed position. Swallowing, yawning, or lower jaw movement causes contraction of the tensor and levator veli palatini muscles, which open the eustachian tube. Functionally, the anterior channel behaves as a 1-way valve. Air easily escapes the middle ear cavity when ambient pressure is reduced (ascent) but does not readily reenter this cavity when ambient pressure exceeds middle ear pressure (descent). This phenomenon is amplified in those with allergic or upper respiratory symptoms, probably because of edema and general reduced patency. Expanding air escapes from the middle ear into the back of the pharynx while climbing, thereby equalizing air pressure. This is normal physiological functioning. Problems typically arise during descent, when the eustachian tube collapses and air is prevented from reentering the middle ear. Failure to equalize pressure causes retraction of the tympanic membrane and severe pain. The flying literature is filled with anecdotes of pilots who had to abort landings because of the severe pain associated with ear blocks. The phenomenon of delayed ear blocks occurs in aviators (passengers or crew) who breathe 100% oxygen. This problem often affects those who fly late at night and then go to sleep, and it may affect patients who breathe 100% oxygen during transport, especially if heavily sedated. Oxygen-rich air remains in the middle ear cavity after landing, and slight negative pressure keeps the eustachian tube closed. Several hours after flight termination, local tissues absorb the oxygen, and the negative pressure differential is increased. The patient wakes up in the middle of the night with otalgia and a retracted tympanic membrane. Preventing an ear block Prevention, recognition, and early reversal are the mainstays of treatment for barotitis media. Fuel and weather permitting, gradual descents permit more complete equalization of middle ear and sinus pressures. In pressurized aircraft, maintaining high cabin pressure (low-altitude equivalents) and slowly pressurizing the cabin in advance of descent are useful techniques. Sleeping during descent is risky because people swallow and yawn less when asleep, and early warning signs of mild ear discomfort may go unnoticed until a full ear block develops. For this reason, some airlines maintain a policy of waking sleeping passengers prior to descent. Infants who cry inconsolably during descent often are troubled by ear block. Nursing infants should be encouraged to suck on a pacifier during descent to help maintain eustachian tube patency. Reversing an ear block Ear block develops in a vicious cycle; the greater the middle ear/atmospheric pressure differential, the more difficult it is to restore eustachian tube patency. Pseudoephedrine, the Valsalva maneuver (ie, exhaling against a closed mouth and pinched nose), yawning, and gum chewing all have been attempted to restore pressure to the middle ear after an ear block develops. Physiologically, all of these maneuvers are designed to restore eustachian tube patency momentarily to permit equalization. Some advocate performing the Valsalva maneuver with the neck laterally flexed to one side then the other in an effort to stretch and straighten the eustachian tube. Some airline attendants and flight medics use a technique called politzerization to help those with ear blocks. Using a Politzer bag, which is essentially a reverse suction bulb, the medic attempts to force air into the nasopharyngeal opening of the eustachian tube.

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PART IV - SOME GYNAECOLOGICAL PROBLEMSThe use of the oral contraceptive pill (OCP) has been associated with an increase in the incidence of vascular thrombosis, thrombo-embolism, cerebrovascular accident, hepatic adenomata, biliary disease, and hypertension. The risk of the vascular complications is heightened if the woman taking the pill is also a smoker. OCPs may also cause personality, mood, and weight changes in certain susceptible individuals. Agents within an OCP may also interact with other medications. A separate but related consideration is that of the incidence of foetal damage or spontaneous abortion induced by the flight environment. A first trimester foetus undergoes much of the organogenesis and differentiation that is so sensitive to external noxious influences such as radiation and chemical toxins. T here is the theoretical potential for the rigours of the flight environment to cause an increased incidence of foetal malformations or spontaneous abortions in pregnant female aircrew. The limited research available tends to consider air-hostesses rather than female pilots and does not seem to support the hypothesis of an increase in abnormal pregnancy outcomes. Air hostesses do suffer an increase in spontaneous abortion when compared to other women but not when compared to other working women. There is an increased incidence of past spontaneous abortion amongst pregnant air-hostesses but this may be due to a selection bias where a previous successful pregnancy selects an individual out of the test population.DEEP VEIN THROMBOSIS AND PULMONARY EMBOLISM ********THIS IS THE MAIN TOPIC WHICH I WANTED TO PRESENT SINCE SEVERAL PASSENGERS ARE SUING PHYSICIANS AND AIRLINE COMPANIES FOR NEGLIGENCE. I HOPE FOLKS UNDERSTAND THE REAL PROBLEM!!!!!Deep vein (or venous) thrombosis is a condition in which a small blood clot (thrombus) or clots (thrombi) develop(s) in the deep veins usually of the leg. The condition itself is not dangerous, but the complication of pulmonary embolism (venous thromboembolism

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PART VI - SOME TRIVIAPATIENT FITNESS FOR FLIGHT. (Very very very brief!!!)CardiovascularSupplemental oxygen is strongly recommended for cardiac patients even when not required on the ground. Hypoxic stress may aggravate or precipitate cardiac ischemia. Acceleration and climb-out can be dangerous if blood pressure and cardiac output are tenuous and if the patient is positioned with the head toward the front of the plane. Longitudinal acceleration on the takeoff roll, combined with nose-high pitch on climb-out, creates significant venous pooling and preload reduction can be significant in those with unstable hemodynamics; thus, supine patients typically are placed head rearward. Landing stresses are usually less worrisome, and nose-high landing attitude offsets deceleration forces to some degree. PATIENTS WITH A RECENT HEART ATTACK (WITHIN 30 DAYS) ARE USUALLY PROHIBITED FROM FLYING.Neurological Usually, patients with brain injury are best positioned with the head rearward for takeoff and forward for landing. This positioning reduces the impact of caudal acceleration forces and decreased perfusion. The benefit of greater perfusion, however, must be weighed against the risk of increasing intracranial pressure. At cabin altitudes of 4,600 m (15,000 ft) or below, low PCO2 effects predominate, and cerebral vessels are constricted. Above this altitude, low PO2 effects predominate, and cerebral blood flow increases. (An increase in cerebral blood flow means higher intracranial pressure)PulmonaryUntreated pneumothorax is an absolute contraindication to flight unless sea-level cabin pressure can be strictly guaranteed. This is usually impossible; thus, placement of a chest tube with Heimlich valve is indicated. Patients with recently removed chest tubes should wait 72 hours prior to air transport because even radiologically undetectable pleural gas can expand to significant volumes in flight. People with bullous emphysema are at risk for rupture and pneumothorax at altitude, especially during rapid loss of cabin pressure. When transporting intubated patients, some authorities recommend inflating endotracheal tube cuffs with saline instead of air to avoid gas expansion problems at altitude. THAT IS IT! IF YOU HAVE ANY COMMENTS/SUGGESTIONS, PLEASE E-MAIL ME(PREFERABLE) OR POST HERE AT THE FORUM. MANY THANKS TO AVSIM STAFF, MODERATORS AND FORUMS MANAGER WHO MADE ALL THESE GREAT FORUMS ENJOYABLE.HAPPY FLYING.http://ftp.avsim.com/dcforum/User_files/3daf27346bd8c095.jpg

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Jinesh, You bring up some interesting points about the cabin pressure being at 8000 feet,I travel on business with 8 people. Two of those people are smokers.We travel by air and by tour bus, being a rock band. What my question is, why do smokers, feel the altitude traveling by land more than by air? We are based out of an altitude of 120 feet of where we live, but when we get above a land altitude of 3 to 4 thousand feet plus, the singer who smokes a little and the bass player who smokes alot complains of not being able to breath comfortably while sleeping.They never complain while in an aircraft for long periods of time, other than they can't smoke. Is it a situation of sitting compared to a lying down in a hotel/bed/tour bus bunk/position?Any thoughts on this?CuriousBrianMontrealCanada

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Very interesting and informative. I've been flying since birth 33yrs and I've had the occasional ear blockage but it has never really bothered me until... I was flying from Orlando to Minneapolis onboard a Northwest Airlines DC-10 and I did notice we were decending steeply, but the pain was damn near unbearable - I finally had to stand up and walk to the bathroom just to get my mind off the pain. It's good to understand what causes the pain. Also interesting information on traveling with kids I have a two year old and a new born so very relevant. Thanks for the info!!

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Great info Jinesh!! Wow... so much info!I'm happy to say that I don't feel any ear pain while flying. But I was reminded by something. You mentioned Sinuses, briefly. The last time I flew, I had terrible terrible sinus pain for the whole part of the pressurized flight. The capt. said that we were flying at 38000ft. It was a 737-800.I have no idea if 38,000ft is a normal height... but sounds quite high for a European flight. Anyway... does anyone know how to realease sinus pressure during flights?Cheers,Simon.

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Dear Mr. Brian,Thank you very much for your question. Your observation and reasoning of this common clinical problem is very commendable. Before I go into describing the details, here are some essential pathophysiology basics which will help you to understand my explanation better.FACT 1: How does the heart pump?The left side of the heart pumps blood through the arteries to all parts of the body. Blood returns to the right side of the heart through the veins, PASSES THROUGH THE LUNGS WHERE THEY ARE OXYGENATED and then pass sequentially to the left side of the heart and the cycle is repeated.FACT 2: What is mountain sickness?Many of us who ascend rapidly to high altitude without any protective mechanisms experience WITHIN 8-24 HOURS, headache, irritability, insomnia, breathlessness, nausea and vomiting. This is ACUTE MOUNTAIN SICKNESS. It has been attributed to CEREBRAL OEDEMA (Low oxygen at high altitudes causes dilatation of blood vessels in the brain leading to leakage of fluid into the brain) and PULMONARY OEDEMA (The mechanism of which is still not known). Pulmonary oedema can be due to a multitude of cause including morphine overdose or due to Congestive Cardiac Failure as we shall see in FACT 4.If the ascent has been gradual, we may still experience milder symptoms - CHRONIC MOUNTAIN SICKNESS.- this is more or less same as acclimatization (FACT 3)FACT 3: What is acclimatization?This refers to the compensatory mechanisms which operate OVER A PERIOD OF TIME (NOT SUDDENLY!!!) to increase altitude tolerance. Some of these are as under. (1) Hyperventilation : In an attempt to get more oxygen, you tend to breathe faster - but this will wash out all the Carbon di oxide (CO2) and produce RESPIRATORY ALKALOSIS - tingling and numbness around the lips etc. (2) Increase in the number of red blood cells which will increase the viscocity of blood. Increase in blood viscocity means that the heart has to pump harder to force the viscous blood rather than the fluid blood we had previously. (3) Lung membrane becomes more permeable to gases. (4) Increase in the number of capillaries to tissues.The ability of your muscles both skeletal and cardiac is greatly reduced at high altitudes due to lack of oxygen.FACT 4: How smoking makes fun of these compensatory mechanisms?(1) Cigarette smoke causes constriction of the AIRWAY smooth muscles and prevent normal oxygenation.(2) Cigarette smoke causes constriction of the VASCULAR smooth muscles and blood flow becomes sluggish. You must remember that blood flow has already becomes sluggish from an increase in the number of red blood cells. This causes a lot of blood to stagnate in the lungs and patient starts feeling breathless.(3) Cigarette smoking in conjunction with alcohol causes cholesterol to deposit on your arteries - this means your heart has to pump against greater resistance - finally your heart has started failing. This generates tremendous backpressure (because the heart is not able to pump blood forwards) which is transmitted to the lungs and they start getting congested (filled with) blood. With time fluid oozes out from the blood vessels into lung tissue and breathlessness increases. This is called CONGESTIVE CARDIAC FAILURE with superimposed PULMONARY OEDEMA (Fluid in the lung tissue.)(4) Problems 2. and 3. add up together to increase breathing difficulty.FACT 5: What is the difference between sleeping while lying down and while upright?When you stand upright, blood has to return to the heart AGAINST GRAVITY which is made possible by contraction of the calf muscles while we move about. While sitting or sleeping upright as in aircraft seats, it is the same - blood has to rise up against gravity which is facilitated if we move a bit.When we sleep on our beds in home, sweet home, the situation is different. Blood can flow without hindrance to the heart since there is no need to overcome gravity. This means that the venous return to the heart increases while we are lying down. A NORMAL PERSON can EASILY TOLERTE THIS INCREASE IN BLOOD FLOW TO THE HEART. But our friends who smoke and who have a failing heart, just cannot tolerate this increase in blood flow and they feel breathless. INDEED, THEY OFTEN VOLUNTEER THE INFORMATION THAT THEY CAN SLEEP BETTER WHEN IN THE UPRIGHT POSITION - a condition called ORTHOPNOEA.So let us come back to your questions.(1) Why do smokers, feel the altitude traveling by land more than by air?All of us whether smokers or non-smokers, feel the change in altitude more by land than by air. This is because, the air cabin is pressurised at ambient pressures for our comfort, temperature adjusted accordingly and oxygen supply also adjusted accurately. This is in sharp contrast to land travel where no such protective measures are taken. Indeed, if you have been living at high altitudes for a long time (say 2 to 3 weeks), you will not even have the slightest difficulty. Since all of you are based at an altitude of only 120 feet above the sea level, this will not evoke any compensatory mechanisms.(2) They never complain while in an aircraft for long periods of time, other than they can't smokeFACT 5 GIVES US THE ANSWER.(3) The singer who smokes a little and the bass player who smokes alot complains of not being able to breath comfortably while sleeping AT 3000 TO 4000 FT.FACT 5 GIVES US THE ANSWER(4) Is it a situation of sitting compared to a lying down in a hotel/bed/tour bus bunk/position?INDEED!! YOU GUESSED IT RIGHT.(5) Any thoughts on this?Mountain sickness will make you breathless whether you are upright or flat. But only Congestive Cardiac Failure with pulmonary oedema can make them breathless when lying down flat and GET RELIEVED by sitting up. A thorough physical examination will show at the time of attack of breathlessness - leg swelling, distended neck veins, enlarged liver and fine crepitations over the chest if you auscultate with the stethescope.I STRONGLY RECOMMEND A DETAILED WORK UP OF YOUR FRIENDS WITH THEIR PHYSICIAN AS SOON AS POSSIBLE AND OF COURSE A RESOLUTION ON THEIR PART TO GIVE UP SMOKING FOR GOOD.As always, any doubts, you are most welcome to ask.Kind regards,Dr. Jinesh Thomas"THE CIGARETTE IS ONE HELL OF A PIPE BUDDY! YOU CAN SEE THE FLAME AT ONE END AND THE FOOL AT THE OTHER END"

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Dear Mr. Simon,Hope you will find this information regarding paranasal sinuses very useful.THE SINUSES - WHAT ARE THEY?The sinuses are air filled chambers in the skull - they serve to make it light and helps to add resonance to voice which is why when we have sinusitis our voice is altered. They open into the back of the nose through thin tunnels of bone.The paranasal sinuses are just like your tympanic cavity (middle ear). The air within it expands on ascent and contracts on descent. When the sinuses are blocked during a cold due to build up of secretions and oedematous mucosa, the blocked air will not be able to move to and fro to equalise witht the outside air pressures. The build up of pressure will cause pain in the forehead, cheek, deep within the head accompanied with profuse watering of the eyes. So you can understand why I ground some Indian Airforce Pilots on this context till they are fit to fly again!!! It may be of interest to you to know that German dive bombers in WWII had myringotomies (small incisions made in the ear drum) to help them equalise their ear pressures while they performed their acrobatics!!!!!Same thing goes with our digestive system. The human body contains fairly large amounts of gas (including MOSTLY AIR WHICH WE SWALLOW DURING MEALS as well as gases formed in the stomach and intestines during digestion). Expansion of stomach or intestinal gas can lead to discomfort, hence it is better to avoid consuming "gas-generating" food such as pulses (short chain oligosaccharides are the culprit), beans, cabbage, carbonated drinks and beer before your flight. Alcoholic drinks in addition promote dehydration which is not very welcome as I have mentioned earlier. You may need to remove your contact lenses if they become irritated in the dry air and you can use moisturizers to refresh your hands and face. Dry air can aggravate allergies or asthma, so take the same precautions as if you were in any similar climateIf you or your fellow passengers get this sinus barotrauma, treatment is much the same as middle ear problems. Physicians often discourage their patients from flying till they are all right but this is often not practically possible. First try nasal decongestants - this will reduce the swelling enough to let the air vent. AS AGAIN USE MEDICATION ONLY AT THE DISCREETION OF A MEDICAL PRACTIONER. ASSOCIATED MEDICAL CONDITIONS HAVE TO BE TAKEN INTO ACCOUNT. The Valsalva manoeuvre (blow forcibly against a closed mouth or nose) does not work well with the sinuses as they do with the ear but it is worth trying. Pseudoephedrine which I had mentioned earlier has recently fallen into disrepute since there were reports of (not in INDIA but elsewhere) increased incidence of stroke in FEMALES who took them. Evidence in males is lacking. It is too early to speculate though since it is an over the counter drug and has consistently produced good results. Catching A ColdMicroorganisms do not pass through the filters of the highly efficient air recirculation systems on today 's jets. The system delivers a mix that is one-half outside air and one-half filtered recirculated air. It normally produces between 14 and 20 cubic feet of air per person each minute. As a result, the air supply in the cabin is essentially sterile and particle-free. However, whenever groups of people are together, there is the potential for diseases to spread. Passengers who become ill during or after a f light may have gotten the disease either from another passenger or from exposure before traveling. It is a good idea to wash your hands and minimize touching your eyes, nose, and mouth while you are traveling.Hope it helps.Regards,Dr. Jinesh Thomas

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Dear Mr. Etienne,Here is some info on Cabin altitude. CABIN ALTITUDE PRESSURE - THE HOW AND WHY.At the normal cruising altitude of heavy commercial jets, 28 to 34, 000 feet, barometric pressure outside the aircraft is insufficient to sustain life. So when the aircraft climbs, the barometric pressure inside the passenger cabin and cargo holds is allowed to decrease, but only to a pressure equivalent to 6,500 feet, or 8,000 feet with some older jets. This allows passengers and livestock to breathe quite easily. Ideally, it would be nice if the internal cabin pressure could remain the same as that at sea level (no popping ears!), but this would put a much greater pressure load on the fuselage, requiring stronger and thus heavier construction.So a compromise is struck: When the aircraft is flying at, say, 31,000 feet, the cabin and cargo hold altitude never exceeds a barometric pressure equivalent to 8,000 feet. Overall fuselage weight is thereby minimized, but you the passenger can still breathe easily while eating your in-flight meal etc. The percentage of oxygen in cabin air remains virtually unchanged. There is more than enough oxygen available for human consumption at cabin altitudes up to 8000 feet, unless an individual is suffering from certain diseases of the heart or lungs (which I have mentioned before in brief). In this case, supplementary oxygen can be provided if prior notification is given to the airline. Most airlines will not permit you to carry YOUR oxygen masks for safety/security reasons. They are available on board on payment of a nominal fee.Hope this helps.Regards,Dr. Jinesh Thomas

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